With object storage systems being increasingly recognized as a preferred way to expose one’s storage infrastructure to the web, the past few years have witnessed an explosion in the acceptance of these systems. Unfortunately, the proliferation of available solutions and the complexity of each individual one, coupled with a lack of dedicated workload, make it very challenging for one to evaluate and tune the performance of different systems. To help address this problem, the authors present the Cloud Object Storage Benchmark (COSBench). It is a benchmark tool that they have developed at Intel with the goal of facilitating both performance comparison and system optimization of these systems. In this paper, they describe the design and implementation of this tool, focusing on its extensibility and scalability.